High temperature curing matrix resins such as bismaleimide (“BMI”) and benzoxazine (referred to collectively herein as “the high temperature cured resins”) recently have been used to fabricate tooling to make composite parts for a variety of industries, such as the avionics and aerospace industries. BMI and benzoxazine exhibit higher glass transition temperatures than epoxy resins that traditionally have been used in such composite tooling. In this regard, the high temperature cured resins provide higher durability than epoxy resins and are able to be machined unlike epoxy resins.
However, the manufacture of composite tooling using BMI and bismaleimide has been costly and time intensive. A typical manufacturing method for making tooling used to make parts for, for example, the avionics industry is illustrated in FIGS. 1-3. Referring to FIG. 1, the method for making a tool begins by making a master mold 10. The master mold typically is formed from an inexpensive and easily cut material, such as medium density fiberboard or foam, which is cut, such as by computer numeric control (CNC) machining, to have a surface 12 that is identical in topography to a surface of a part desired to be manufactured from the tool, such as, for example, an aileron for an aircraft. An intermediate mold 14 is formed overlying the surface 12 of the master mold 10 by arranging a number of low-temperature cured epoxy resin prepreg plies thereon. The intermediate mold 14 is formed usually at thicknesses of about 6.4 millimeters (mm) (0.25 inches). The intermediate mold 14 is cured at relatively low temperatures, typically at temperatures in the range of 48 to 60° C. (120 to 140° F.). A supporting substructure 16 then is attached to the intermediate mold 14 using fixing methods such as adhesives and laminate tie plies. The master mold 10 is separated from the intermediate mold 14 and the intermediate mold next is post-cured, typically at temperatures in the range of 176 to 191° C. (350 to 375° F.).
Referring to FIG. 2, a laminate layer 18 of BMI or benzoxazine prepreg plies is formed overlying the intermediate mold. The laminate layer is heated, typically to a temperature in the range of about 176 to 191° C. (350 to 375° F.) depending on the BMI or benzoxazine used, to cure the laminate layer 18. The resulting cured laminate layer 18 typically has a thickness of about 9.525 mm (0.375 inches). A substructure 20 is affixed to the laminate layer 18 using fixing methods such as adhesives and laminate tie plies forming a tool 22. The tool 22 is removed from the intermediate mold 14 and is post-cured at a temperature typically in the range of 204 to 216° C. (400 to 420° F.) depending on the BMI or benzoxazine prepreg plies used. Referring to FIG. 3, as the laminate layer 18 has a surface 26 that is the negative of the surface 12 of the master mold 10, a part 24 then can be formed using the tool 22 with the part having a surface 28 that mimics the surface 12 of the master mold.
The above-described traditional method provides a number of drawbacks. The method requires four heating cycles to cure the intermediate mold and the laminate layer. Each heating cycle adds time to and increases cost of the manufacturing of the composite tool. In addition, the intermediate mold 14 and the laminate layer 18 are formed with relatively large thicknesses so that each layer has a relatively uniform thickness with minimal variation across the layer. But large thicknesses of these layers not only drive up the tool's costs but also result in heating variations during curing of the parts. The method also requires the use of two substructures 16 and 20 and the substructures are positioned on top of the respective layers. In this regard, warping, twisting and racking of the substructures and the respective layers relative to each other are introduced during fabrication when the substructures are affixed to the respective layers.
Accordingly, it is desirable to provide methods for fabricating composite tools that utilize a reduced number of heating cycles. In addition, it is desirable to provide methods for fabricating composite tools that utilize relatively thin laminate layers. It is also desirable to provide methods for fabricating composite tools that utilize fewer substructures. It is further desirable to provide composite tools that are made from such methods. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.